As a cap on a bottle-shaped container, a combination of an inside plug for sealing and an overcap, which is an upper closure, is generally known (for example, refer to Japanese Patent Application Laid-open No. H8-58816). With the kind of cap, opening or unsealing is carried out by pulling a pull-ring attached to the inside plug diagonally in the opening direction after opening the overcap.
Further, a bottle cap, which has a material storage part for storing a powder or other such material, and which releases the material inside the bottle by causing the bottom lid of the raw material storage part to drop out due to the opening operation, is known (Japanese Patent Application Laid-open No. 2005-88997).